This invention relates generally to the field of electrostatic printing processes, and more particularly to an improved coating applied to an elastomeric charging blade pressed against a developing roller which forms part of the developer apparatus used to develop an electrostatic image normally using a single component toner.
One component toner, also known as monocomponent toner, is widely used in electrophotographic printers. The toner may also contain other additives used to improve flow characteristics and to control charging. The toner is triboelectrically charged by the friction developed in its movement through the developer apparatus. This friction occurs at the developer roller surface, which is usually textured, and is increased by the use of an elastomeric blade placed in contact with the developer surface. The elastomeric blade also meters the layer of toner on the developer roller prior to image development.
Developer rollers used with monocomponent toners can create unequal charge distribution among different size toner particles. U.S. Pat. No. 4,989,044 discloses the variation in toner charge and related particles in the toner layer on the developer roller. The solution to equalize the charge, according to this patent, is to use a conductive coating on the developer roller surface. U.S. Pat. No. 5,027,745 discloses that the conductive coating described in U.S. Pat. No. 4,989,044 is usually short lived. This short life is even more pronounced with developer rollers using elastomeric blades pressed against them to increase the friction on the toner passing over the developer roller surface. The elastomeric blades significantly increase the wear of the developer roller surface.
The need for a conductive coating to equalize the toner charge is of particular importance in developer systems that use toner projection development, a process which is described in U.S. Pat. No. 4,292,387. The AC voltage applied to the developer roller causes sorting of the toner particles by size with the smaller higher charged particles migrating to the inside of the toner layer on the developer roller. This toner particle sorting by size results in lower image density and developer roller ghosting.